The present invention relates to a gas turbine stationary blade and, more particularly, to a gas turbine stationary blade of such a construction that a thermal barrier coating (TBC) can be applied to the blade surface and cracks can be prevented from being made by thermal stresses at the shroud portion of the blade.
FIG. 4 is a perspective view of a conventional gas turbine stationary blade, and FIG. 5 is a plan cascade view of a plurality of blades. One inside shroud 11 and one outside shroud 12 are provided with respect to one stationary blade 1 as shown in FIG. 4.
The stationary blade 1 has a construction such that a seal plate (not shown) is put between the shrouds, which are adjacent to each other, by which the leakage of cooling air is decreased. When a single blade construction, in which blades are divided separately, is used because of the need for applying a thermal barrier coating to the blade surface, the number of portions where seal plates are inserted increases, resulting in increased leakage of cooling air.
In order to decrease the leakage of cooling air, several stationary blade can be cast as an integrated, one-piece segment, or single cast blades can be joined by welds into an integrated segment. In these cases, however, a thermal barrier coating cannot be applied to the whole surface of the blade.
As describe above, the decrease in leakage of cooling air caused by blade division is prevented conventionally by one-piece casting of a plurality of stationary blades as an integrated segment or by welding individual cast blades into an integrated segment. However, if singly cast blades are welded into an integrated segment, high thermal stresses cannot be relieved by the temperature difference between the dorsal side and ventral side of blade, so that the potential for the generation of cracks in the shroud is increased.
With the recent increase in gas turbine inlet temperatures, thermal barrier coatings etc. are applied to the blade surface by spraying, using a coating gun, to reduce the thermal load of blade surface to the utmost. In this case, if multiple stationary blades are cast as a one-piece cast integrated segment, or if singly cast blades are welded into an integrated segment, the coating gun typically does not enter a curvedly space formed between the blades, so that the coating cannot be readily applied to the whole blade surface.